This invention relates to a network system which includes a managing unit and a managed unit which is managed by the managing unit and which may be therefore called a network management system. It is to be noted throughout the instant specification that the managed unit is practically a communication package (simply called a package) which is located in a slot formed within a housing and which will be often referred to as a network unit and that the managing unit may be practically an agent. At any rate, the agent is located between the manager and the communication package, namely, the network unit and is operable to execute a management operation instead of the manager.
A conventional network system of the type described includes an agent connected to a manager and a plurality of network units communicable with the agent. In order to carry out management operation, a command is issued from the agent to each of the network unit while a response is sent from each of the network units to the agent in response to the command. With this structure, each of the network units must have an interface which can interpret the command, collect a data signal to be managed (namely, a managed data signal), and form a response format. Therefore, the interface is intricate in structure.
In addition, the agent carries out polling operation to each of the network units to acquire the managed data signals from the network units by delivering a specified command to each network unit. The managed data signals are sent back to the agent as the responses.
Herein, it is to be noted that a restricted amount of the managed data signal alone is extracted each time when the single polling operation is carried out. Accordingly, the polling operation should be repeated again and again to extract a great deal of the managed data signals from the network unit. This degrades a transmission efficiency.
Alternatively, a proposal has been made about a network system or a network management system which is described in Japanese Unexamined Publication No. Hei 5-204811, namely, 204811/1993, and which has an agent and a network unit. Such a network system proposed is effective to quickly transmit an alarm signal from the network unit to the agent when a fault takes place in each of the network units. In addition, it is also possible to quickly collect the alarm signal from each network unit and to transfer the alarm signal to the manager.
For this purpose, each of the agent and the network unit includes a connection oriented communication interface and a connectionless communication interface. In addition, the connection oriented communication interface and the connectionless communication interface of the agent are communicable with those of the network unit, respectively. With this structure, the connection oriented communication interfaces in the agent and the network unit are used for communication which is triggered by the agent and which is made, for example, to acquire data signals of the network unit by the agent. On the other hand, the connectionless communication interfaces in the agent and the network unit are used for communication which is triggered-by the network unit and which is made, for example, to urgently or emergently transmit the alarm signal from the network unit to the agent. Thus, emergent communication can be carried out between the network unit and the agent by the use of the connectionless communication interfaces.
Herein, it should be considered in connection with the above-referenced network system that occurrence of an emergent event, such as occurrence of a fault, must finally be reported to the manager which is connected to the agent. However, two different kinds of the interfaces should be prepared in the above-referenced network system in the manager, the agent, and the network unit. This brings about complexity of the network system. In addition, each of the connectionless communication interfaces has a low reliability, as mentioned in the referenced Japanese Unexamined Patent Publication and acknowledgement should be made each time when communication is carried out through the connectionless communication interfaces.
In general, managed data signals acquired by the managing unit are preferably classified so as to effectively manage the managed data signals. However, no consideration is made at all about different attributes of the managed data signals.
Moreover, it is preferable that the alarm signal is quickly transmitted through the agent to the manager, regardless of a load imposed on the agent. However, the transmission of the alarm signal-is practically delayed as the load imposed on the agent becomes heavy.